The present invention relates to an optical filter of the optical devices used in an optical communication, more particularly, to a tunable Fabry-Perot filter and a method for fabricating the same.
Technology of making an optical filter, particularly, technology on a tunable optical filter, is related to tunable Fabry-Perot filters, a micro machined device, a Mach-Zehnder interferometer, a fiber bragg grating, acousto-optic tunable filters, electro-optic tunable filters, an arrayed waveguide grating (AWG), an active filter, and ring resonator tunable filters. Description on such tunable filter is well given in pages 50-55 of the IEEE Communication Magazine issued on December, 1998, by D. Sadot and E. Boimovich, and entitled xe2x80x9cTunable Optical Filters for Dense WDM Networksxe2x80x9d.
The technologies of the tunable Fabry-Perot filters are largely classified into two kinds. First thing is a method for adjusting optical thickness of a cavity medium between optical fibers each having a high-reflective cross-section by using a piezo-electric technology (see pages 781-783 of Electronics Letters, Vol. 23, issued in 1987 by J. Stone and L. W. Stulz and entitled xe2x80x9cPigtailed high finess tunable fiber Fabry-Perot interferometer with large, medium, and small free spectral rangexe2x80x9d). The other is a technology of tunably filtering by deriving a variation of refractive index due to a change of polarized light characteristics when an electric field is applied, using Ferroelectric Liquid Crystal as a medium between optical fibers each having a high-reflective cross-section (see pages 379-381 of IEEE Photonics Technology Letters, Vol. 7, No. 4, issued in 1995 by A. Sneh and K. M. Johnson and entitled xe2x80x9cHigh-speed wavelength tunable liquid crystal filterxe2x80x9d).
However, the method using piezo-electric technology for adjusting the thickness of the medium makes it difficult to align the optical fibers with each other and has many difficulties in a manufacturing process, since it is configured to use ferrule and a sleeve in aligning the optical fibers.
The technology using Ferroelectric Liquid Crystal as a medium also has many difficulties in aligning and manufacturing processes, because an improvement of the filtering speed is obtained through changing the alignment of the liquid crystal by applying the electric field thereto.
It is, therefore, a primary object of the invention to provide a tunable Fabry-Perot filter having a broad free spectral range (FSR), good finess, narrow 3-dB peak bandwidth or narrow full width at half-maximum, and a widened tuning range by using a thermo-optic effect of silicon and polymeric material, being easy to manufacture and to align optical fibers, and capable of being used for dense wavelength division multiplexing (WDM).
In order to achieve the object, the present invention provides a tunable Fabry-Perot filter including V-shaped grooves for aligning optical fibers each having a high-reflective cross-section, a thin-film medium having a resonant cavity of a high thermo-optic coefficient, and a thermal electrode formed on or between the thin-film medium.